The following invention relates to ballbearings, and in particular, an apparatus for mounting and precisely aligning such bearings.
Contained in a ballbearing are inner and outer races, separated by a plurality of balls that roll in opposed grooves in each of the races. The inner race typically receives a shaft or journal, and the outer race is mounted on a structure that supports the shaft load. So as to achieve maximum bearing service life, the inner and outer races should be properly aligned so that the two races are parallel to one another with respect to a common center line. If however, the races are not parallel, the path the bearing balls follow as they move around the shaft is not on a plane perpendicular to the common center line. As a result, the balls move from one side of the race groove to the opposite side and therefore have both movement around the shaft axis and back and forth parallel to the common center line. This condition is often referred to as bearing angular misalignment and can produce premature bearing spalling, which results from the combination of bearing angular misalignment and the consequentual reduction in ball loading area. Another product of unwanted bearing angular misalignment is smearing. That occurs as the balls move from loaded to unloaded positions in the race grooves. Hence, the wear on the bearing components from bearing angular misalignment is thus significantly accelerated, reducing the life of the bearing.
If the outer race support is on a plane that is substantially nonperpendicular to the shaft axis, a bending moment is produced between the inner and outer races. As a result, the bearing will be angularly misaligned and a torque relationship between the inner and outer races will also exist, which is transmitted through the balls to the races along the plane of the shaft axis, that being the bearing common center line. The engendered nonparallel relationship between the race grooves, combined with the increased ball loading arising from the reduced contact area and bending moment, enlarges the destructive forces exerted on the balls and race grooves, further accelerating spalling and smearing. In addition, the increase in loading on the bearing together with the reduction in the ball load carrying surface, increases the chances for damage to the bearing from shocks and blows sustained during its installation and subsequent storage. This is generally referred to as brinelling, and results from the plastic flow in the race grooves from the excessive stresses applied thereto by the balls when they are stationary. Consequently, angular misalignment, when combined with inter-race torque, further increases bearing wear and the chances of premature failure.
In the prior art, self-aligning bearings are used to compensate for angular misalignment. These bearings are typically cut to have spherical outer races that swivel in the bearing supporting structure. In small electric motors, for example, the socket is on a removable motor end plate. When the plate is mounted on the motor frame, the socket permits the plate to swivel with respect to the shaft and bearing, which eliminates at least a portion of the inter-race torque that otherwise arises from the bending moments if the plate did not swivel. Nevertheless, the inter-race torque is not completely eliminated because a certain amount of friction exists between the outer race and the socket which generates a moment opposing the swivel movement of the plate. Hence, for the plate to swivel, the moment must be overcome by an equal and opposite moment exerted between the races through the balls. The opposing moment thus creates inter-race torque, which is present after the plate swivels. Furthermore, the opposing moment arises from the angular misalignment between the races, and consequently, the same results are produced as in the case of nonself-aligning bearings, specifically: spalling and brinelling. Needless to say, these negative results are particularly significant if the friction between the outer race and the socket is high, since that increases the moment and concomitant torque.
Consequently, self-aligning bearings simply limit rather than eliminate the inter-race torque condition. And of equal importance, even if the inter-race torque is small the races are at their maximum angle of misalignment; that is, the balls are pressed against the opposite sides of the grooves on diametrically opposite sides of the bearing. It is particularly noteworthy that angular misalignment is present in all prior art self-aligning bearings to some degree, and hence the path of the balls as they roll is skewed or nonperpendicular to the shaft axis, which, as mentioned earlier, substantially increases the wear on the bearing parts.
So it can be observed that although self-aligning bearings can serve to reduce the torque between the inner and outer races arising from the bending moments, they do not necessarily limit it to allowable limits. Of equal importance, because traditional self-aligning bearings do not completely eliminate the inter-race torque, angular misalignment is not eliminated. Finally, since the outer race on such bearings is generally spherically cut, they are considerably more expensive than standard bearings having simple ring-like outer races.